Expert Opinion: Acoustic Privacy

Steve Gardner from the EQUUS Partnership gives us the expert insider knowledge on the hot topic of acoustic privacy.

During the development of our latest Revolution 100 partition system – a breakthrough in acoustic performance, achieving up to Rw52dB – we realised that the specifics of acoustic privacy are something of a dark art for most people.

With this in mind, we recently caught up with The EQUUS Partnership’s Steve Gardner, who co-founded the fully independent acoustic consultancy in 1993.

EQUUS has always been dedicated to providing high quality practical advice, able to provide direction on all aspects of noise and vibration control – from the conceptual pre-planning stages all the way through to final commissioning.

Given the golden opportunity at hand, we jumped straight in with Steve to probe his extensive knowledge regarding acoustic privacy.

For those outside the field, it’s not an immediately easy subject to wrap one’s head around, but the basic principle that leads to understanding the crux of the situation is that acceptable levels of acoustic privacy within office environments can usually be achieved with the correct combination of background sound level and partition sound insulation.

“In general, when there is a lack of acoustic privacy between partitioned rooms, it’s usually due to inadequate sound insulation of the intervening partition – unless the background sound levels are particularly low,” says Steve. “This lack of privacy can be caused by many factors, but there are four most common causes in practice.”

Those causes are, in Steve’s words, as follows:

• The partition itself does not provide enough sound insulation across all the speech frequencies – examples of this might be drywall partitions of insufficient mass and/or without any sound absorptive media within the cavity, and, glazed partitions of insufficient mass and/or without an acoustic interlayer.

• Doors within the intervening partition have not been selected with due consideration to their acoustic performance and/or have not been fitted with efficient acoustic seals.

• Either the partitions do not extend full height to the floor slab above, or alternatively, if ceiling void acoustic barriers have been installed, these have not been correctly sealed around services penetrations etc.

• Speech sounds are transmitted via common ductwork services between the adjoining rooms.

Interestingly there’s also a general misconception about quieter office spaces, in that acoustic privacy and comfort levels are often actually made worse if the background noise levels at workspaces are too quiet.

“It’s usually better to design the MEP services noise to provide the correct level of continuous background sound rather than to strive to silence this noise completely,” Steve says. “In situations where this isn’t possible, or where there’s no mechanical ventilation, it’s sometimes necessary for the background sound levels to be elevated by artificial means.”

Which literally means to provide some form of low-level noise, rather than eradicating it altogether.

“In ancient Rome, it was common for water features to be installed in central courtyards to create this effect,” Steve says. “A typical example of this within a modern office environment would be the installation of an electronic ‘sound masking’ system – also known as ‘sound conditioning’, or more colloquially as ‘white noise’. This essentially works by providing an appropriate and adjustable level of background sound across the speech frequency range so that any transmitted speech sounds are effectively ‘masked’ by the background sound that’s produced by the electronic ‘sound masking’ system.”

It’s all incredibly clever and well thought out stuff, and talking to Steve got us to wondering if there’s a base level average for office noise, such as staff conversations and so on.

“In practice, the sound levels in office spaces vary quite significantly depending upon the office occupancy levels and the number of people conversing at the same time,” Steve says. “For example, a telephone call centre would typically have a high number of conversations occurring simultaneously, whereas a higher percentage of people within a design office might only converse between themselves, perhaps only using the telephone occasionally.

“The room sound levels within occupied open plan offices could be as low as 40 dB(A) and as high as 65 dB(A) in noisy environments depending upon occupancy levels, type of office activity, room finishes and so on.”

Interestingly, Steve also says that within meeting rooms, the highest sound levels generally occur during teleconferencing compared to normal face-to-face discussions. And even higher sound levels can occur within cellular offices during hands free telephone usage.

So you know the guy you work with that likes to walk about while on the phone? High sound levels are often due to people moving around the office like him.

“If the project architect is aware that such telephone usage is likely to occur – and if acoustic privacy is deemed to be important by the end user client – then the acoustic specifications for the associated partitioning, doors, acoustic ceilings and so on should all be uplifted to reflect this,” says Steve.

For most projects, the architect’s or acoustic consultant’s specification will require at least the Rw acoustic laboratory performance value to be determined.

“This requires the test sample to be installed within an aperture between an adjoining pair of purpose built, acoustically isolated, test chambers,” says Steve. “These test chambers are built such that they are fully independent from one another to prevent any acoustical energy bypassing – or ‘flanking’ – around the test sample. This ensures that the sound transmission between the two rooms has to occur via the test sample itself. In simple terms, laboratory acoustic testing of architectural building elements such as drywall partitions, single or double glazed partitions, office doors, façade elements and the like are carried out by measuring the difference between the average sound pressure levels generated by high-powered loudspeakers strategically positioned within the ‘source’ chamber and the residual average sound pressure levels occurring within the ‘receive’ chamber.

The way that laboratory and real world tests are carried out are principally the same, in that high-powered loudspeakers are again used to determine the difference between the average sound pressure levels measured within the ‘source’ and ‘receive’ rooms.

“The main difference is that in the real world, the transmitted sound pressure levels will be an accumulation of direct sound transmission – so through the intervening partition – and indirect flanking sound transmission via the flank walls, ceiling tiles, ceiling void, office door, floor void, building façade, services penetrations and so on,” says Steve. “Even with a good quality installation, and reasonable care paid to controlling such ‘flanking’ sound transmission, it’s not uncommon for the on-site R’ acoustic performance to be around 5-7 dB below the equivalent laboratory tested R value. This would normally be taken into consideration by the architect and/or the acoustic consultant when preparing the project acoustic specifications.”

And that, in nutshell, is all you need to know on a first touch point level about acoustic privacy.